Wireless communication networks are well known and increasing in popularity. Mobile terminals, such as cell phones, wirelessly communicate through base stations or node B's in WCDMA that are associated with different cells or sectors in a geographic region, for example. With the increasing popularity and increased competition in wireless communications, system reliability and availability to the end user, is increasingly important.
FIG. 1 illustrates a wireless telecommunication network which defines a number of communication cells (A,B,C,D) each of which is served by a radio base station 11. Each communication cell covers a geographical area, and by combining a number of cells a wide area can be covered. A mobile terminal 12 is illustrated communicating in cell A, and is able to move around in the system 10.
A base station 11 contains a number of receivers and transmitters to give radio coverage for one or more cells. Each base station is connected to network backbone, or core network infrastructure (not shown), which enables communication between base stations and other networks. The example system of FIG. 1 shows one base station per cell.
An important concept in such a system is the cell and its neighbours. During a call a mobile terminal typically moves around among the cells; moving from one to one of its neighbours, repeatedly. A list of known neighbours, the so-called “neighbour cell list” is important for the network to enable reliable handover between cells of a mobile terminal. The purpose of neighbour cell lists is to allow the base stations to give their connected mobile terminals a defined set of cells to measure on.
In existing system like GSM or W-CDMA, the neighbour cell list is broadcasted from the base station to the mobile terminal. The mobile terminal detects cell operating parameters for neighbouring cells. The mobile terminal measures the operating parameters of each neighbour cell and reports those back to the network. When the quality of neighbour cell is considered better than the current serving cell, a handover from the serving cell to the target cell is triggered. The target cell becomes the serving cell for the mobile terminal. The target cell is the neighbour cell having a better quality than the current serving cell.
In Long Term Evolution (LTE) which is a project within the Third Generation Partnership Project to improve the UMTS mobile phone standard to cope with future, the purpose of the neighbour cell lists has been changed as the mobile terminal also referred to as User Equipment (UE) is assumed to decode any Measurement Cell Identity (MCI) on a given frequency. For this reason, neighbour cell lists will not be needed as instructions for the UE to perform measurements. However, there is still a need for each base station to have neighbour cell lists defined, as the base station needs to manage to which neighbour base stations an interface needs to be maintained.
The MCI is a layer 1 identifier for a cell. The MCI is an integer, not long enough to be unique for a Radio Access Network (RAN). When planning the LTE Radio Access Network (RAN), each cell in the network is assigned an MCI. It is assumed that the MCI will have 510 unique values and the MCIs will be reused several times in a large network. The MCIs are distributed so one cell has no neighbour cell with the same MCI as itself and does not have two neighbour cells with the same MCI.
To address the target cell within the Public Land Mobile Network (PLMN) a Cell Identity PLMN (CIPL) is used. The CIPL is a layer 3 identifier for a cell and unique for a cell within the PLMN, typically within a country, or even globally. To establish an interface between a first and second base stations the CIPL is used by the first base station to lookup a transport layer address to the second base station. The lookup could e.g. be performed by a request to a Domain Name System (DNS) name server, which translates the CIPL to the Internet Protocol (IP) address of the second base station and returns the IP address to the first base station.
To prepare for handover between two cells, the UE performs measurements on the received power or signal quality from neighbour cells. The measurement results are reported to the base station and the neighbour cells are identified by a measurement cell identity (MCI) that the UE has received over the air. A handover request is sent from the source cell to the target cell. This request is sent to request resources in the target cell for the UE to be handed over. The target cell then responds with what resources that have been allocated or denies access for the UE.
An automatic, UE assisted, neighbour cell update is being designed for LTE. The UE can here report MCIs for neighbour cells that are unknown to the base station. When this happens, the base station asks the UE to listen to the broadcast channel of the unknown neighbour and report back the CIPL of the neighbour. When the CIPL is known to the base station, the base station can establish communication to the new neighbour.
In the automatic neighbour cell update and in the handover process, the system is vulnerable to UEs reporting faked MCIs and CIPLs to the base station. Consequently, this leads to unnecessary processing, signalling and reservation of resources in target base stations that are not released before the handover later is timed out
Hence there exist a need for a method and arrangements for protecting against UEs reporting fake neighbour cell identity.